Among the most important user operations are those enabling the user to select an object or objects in the image to which further operations subsequently will be applied, e.g. move object, delete object, change object size, etc. The object(s) selectable may include any combination of the following: single characters, single words, lines or paragraphs of alpha numeric text such as found in an image of a page of text; graphic symbols, arrowheads, and geometric figures including lines, circles, and rectangles such as found in graphic drawings; and contiguous isolated strokes, stroke fragments bounded by corners, and stroke fragments bounded by junctions such as found in freehand sketches. The issue of determining which visible items in an image may be made available as selectable image objects is the subject of copending application Ser. No. 08/101,646. In that case, a graphic editing application program maintains a set of selectable image objects during the course of an image editing session. This invention relates to enabling the user from time to time to select for further processing one or more of these objects as conveniently as possible.
An important problem faced by any user-interactive image editing tool is therefore the determination of which object or objects in the image are intended by the user to be indicated by a given set of keystroke and/or stylus gesture commands. Keystrokes are capable of specifying symbolic labels or identities unambiguously, but they are an awkward and unnatural interface for the inherently spatial information contained in a displayed image. Conversely, gestures made with a pointing device are convenient for specifying spatial information in the form of locations on an imaging surface, but can lead to ambiguous specification of the object(s) the user intends to select when several objects occupy the same region of the image. Stylus-based selection can be done, for example only, by the following means: (1) having the user touch the stylus or press a mouse button at a single point in the image whereafter the program selects the object or object's whose location parameter lies at or nearest to that point; (2) having the user touch the stylus or press a mouse button at a point in the image whereafter the program selects the object(s) whose spatial extent most nearly approaches the location specified; (3) having the user draw a closed or nearly closed curve whereafter the program either selects all objects sufficiently enclosed by, or else all objects whose location parameters are enclosed by, the closed curve.
The first two methods fail to support user selection of objects in a very important situation, namely, when the set of objects that the user may wish to select among shares overlapping support at the level of marks in the image. Here, the user may wish to select just a vertical line, just a horizontal line, or an entire corner shape. Specifying a single point on one of these lines does not provide sufficient information to distinguish among the alternatives. Moreover, the third method (encircling intended objects) becomes unacceptable when additional objects are found within the region enclosing the desired objects.